1) The Rage is a combat feature which gives BOTH of the players bonus damage (or Might) every turn.
2) The first turn "n" in which the Rage starts to work, gives +1 bonus damage to both of the players. The next turn "n+1" it gives +2 bonus damage to both of the players... the "n+m"th turn it gives +1+m bonus damage to both of the players.
3) The first turn "n" in which the Rage starts to work is not fixed and can vary with every concrete combat. The game logic decides when it is appropriate to activate the Rage. There are two factors that can speed up the activation of the Rage:
a) The expend of the Collector Decks of both of the players;
b) The number of turns played so far (i.e. if both of the players have short Collector Decks with for example 10 cards each, the Rage will not start right after the expend of the decks)
4) The purpose of the Rage is to handle situations when two heroes cannot kill each other due to high Regeneration and/or Resistance stats.